In the art of joining the ends of metal tubes together, particularly if one or both of the tubes are of an aluminum base alloy, it has been known to provide a solid coating of fluxless solder on a surface of at least one of two tubular elements to be joined together and, after heating the solder to its melting point, to slide the tubular elements aganist each other to disturb to oxide coating normally present on aluminum and thereby facilitate the bonding of the solder to metallic aluminum beneath the oxide layer. However, the necessary sliding fit complicates the operation and requires the expense of manufacturing to close tolerances.
It has also been known to connect tube ends by enlarging one to fit over the other, or by soldering each to a connecting sleeve fitting over both.